'Happy 420'? How Did Marijuana Holiday Get its Name?

Has someone wished you a Happy 420 today? It's probably not because he or she is celebrating Hitler's birthday, although he was born on April 20, or 4/20. More likely they're marking the counterculture holiday unofficially known as National Weed Day.

There are all sorts of rumors about how the term 420 came to be associated with lighting up a joint, but according to the myth-busting website Snopes.com, it was born in the 1970s at San Rafael High School in California, where about a dozen students gathered each day at 4:20 p.m. to smoke pot.

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Over the years, theories about the meaning of 420 have pointed to California's penal code section for marijuana use, the police radio code for smoking pot, and the best day to plant cannabis, according to Snopes.

The issue is gaining ground in the age of President Barack Obama, writes Ryan Grim, the author of "This Is Your Country on Drugs: The Secret History of Getting High in America." In a roundup of efforts across the nation to decriminalize marijuana, Grim says the "momentum is thanks to Obama's announcement that he would not raid shops or patients operating within state laws."